Telemeter.



V. GOLZI & F. BARDELLI.

TELBMETER.

APPLICATION FILED 001:.11, 1909.

Patented Apr. 8, 1913.

6 SHEETS-SHEETI 1+2 s9 15 '26 as V. GOLZI & F. BARDELLI. TELBMETER.

APPLICATION FILED OUT. l1 1909.

Patented Apr. 8, 1913.

6 SHEETS-SHEET 2.

V. OOLZI 6: F. BARDELLI.

TELEMETER.

APPLIOATION FILED 0013.11, 1909.

1,058,556. Patented Apr. 8, 1913.

I GSHEETS-SHEET 3. F iglfi 22 22 v. GOLZI & F. BARDELLI.

TELEMETER.

APPLICATION FILED OUT. 11, 1909.

- Patented Apr. 8, 1913.

6 BBEETS-SHEET 4.

V. GOLZI & F. BARDELLL' TELEMETER.

APPLIOATION FILED 001211, 1909.

1,058,556. Patented Apr.8, 1913. I

6 SHEETS-SHEET 5.

. V. GOLZI & F. BARDELLI.

TELBMETER.

APPLICATION FILED OUT. 11, 1909.

Patented Apr 8, 1913.

6 8HEETSSHEET 6.

M UNITED STATES PATENT OFFICE.

VIRGIIIJIO COLZI AND FELICE BARDELLI, OF TURIN, ITALY.

TELEMETER.

Application filed October 11, 1909. Serial No. 522,123.

To all whmh it may concern:

*e it known that we, nzeruo Conn and l nni'on BARDELLI, both subjects of the King of .ltaly, residing at 18 Via Roma, Turin, ltaly, have in'ventedcertain new and useful Improvements in'Telemeters; and we do hereby declare the following tobe a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertainsto make and use the same, reference being had to the accompanying drawings, and to letters or figures of reference marked thereon, which form a part of this specification.

The present invention refers to a fixed base telemeter by means of which the dis- ".ance of a distant object clearly visible to .he operator may be instantly determined by a single observation at one station.

This present telemeter comprises, a telescopic system, an optical arrangement for measuring distances and a rectifying arrangement. v

The telescopic system comprises two prism telescopes, the objective prisms of which are arranged at an invariable distance apart and constitute the telescope base. These telescopes give by means of a system of erecting prisms two distinctimages of the object observed, said images being observed in the upper half and in the lower half respectively of the field ofa single ocular. The optical arrai'igement for measuring the distance between the two images thus observed in the two halves of the ocular field, render it possible to deduce from said distance, which is so much the greater the nearer observed object, the distance of the objectobserved. This measuring arrangement which has for its purpose to cause the two distinct images observed to coincide with one another or with a mark or line of the ocular cross hairs will be hercinatl tcr described. The telemeter also cmnprises an arrangement for rectifying the position ol the objective prisms with regard to the system of erecting prisms and the ocular. This rectifying system, essentially optical, malors it possible to replace the telemeter elements quickly in their first position in which they were during the first marking (ii-graduation .of the instrument. It permits tlicrehu'c the elimination of all the inconveniences aris ing from the derangements that the instru- Specification of Letters Patent.

Patented Apr. 8, 1 913.

ment may undergo owing tochanges of temperature.

t A form of construction of said' improved telcmeter is shown by way of example in the annexed drawing, lIl'WlllCllZ Figure 1 shows diagrammatically a longitudinal section of a telen'ieter, Figs. 2, 3, 4, 5, 6, show in front View, side view, plan view and two perspective views respectively the system of erecting prisms, Figs. 7, 8, 9, show respectively an object and its images observed in the telemeter during two different conditions of observation, Figs. 10 to 15 are diagrammatic illustrations of the theoretical principle of the micrometer, or measuring device, Figs. 16, 17, are a horizontal section andan elevation respectively of a constructional form of said micrometer,

Figs. 18-22 show avarious positions of the micrometer scales, Fig. 23 is a diagrammatic view illustrating the effect produced by an additional deviating prism used in con'ibination with this telemeter,- Fig, 24 is a section of a constructional form of said deviating prism and its mounting, Figs. 25, 26, are a longitudinal section and an elevation respectively of the central partgof the tclcmeter, Fig. 27 shows in a verti *al section the eyepiece and the system of erecting prisms, Fig. 28 is a perspective diagram of the theoretical principle of the rectifying ar-- rangement, Fig. 29 is a back view oil the system of erecting prisms and additional rectif'ying prisms, Figs. 30, '31, 32, show in longitudinal section, back view and front view, I'QSPOCt-lVOly, the body of the tclen'ietcr with the rectifying arrangen'ient, Figs. 3; 3!, show the ocular field aftc' and before -the rt'a-tification of the ii'istrl'um-ut.

Telescopic systcm.The telescopic system, is inclosed in a casing, preferably of metal having a. small coctlicient of expansion and constituted by two (Figs. 30 to 32) or more (as in Fig. 1) :l'langcc'l bars 1 of T-shapc or;

supported 111 its turn by a foot ofany desired f01l1'l,-\Vl1lle the endrings receive the casings'of the prism Ob cct-ives. The height of the flanged bars 1, the right section of 1 which is preferably T- or U-shaped, diminishes by degrees toward their outer ends at the objectives for the purpose of obtaining The telemeter body is to assure uniformity of temperature in the 'air surrounding the telemeter body and this for the purpose of preventing any unequal expansion of the latter.

At each end of the teleineter body is mounted a light receiver comprising a lens and a prism 5 and 7, and 6 and 8 respectively that make a total reflection, that is each prism has for its base the hypotenuse of an isosceles rectangular triangle. Said prisms 5, 6, the distance between which constitutes the telemeter base, reflect the rays entering through one side and coming out through the other at right angles to their original direction, through the objective lenses 7 and 8 proximate the emergent faces of the prisms. The luminous rays reaching the center of the block 3 are collected by a system of erecting prisms that direct them to the ocular 9.

The system of erecting prisms comprises two totalreflecting prisms 10, 11, crossing each other and attached by means of one of their sides on the lower half of the hypotenuse of a third and larger total reflecting prism 12 (Figs. 2 to 6). This prism system .is mounted in the central part of the block 8, so that the free sides of prisms 10 and 11 are perpendicular to the axis X-X, of the instrument (Figs. 1, 2) and that the point Y, Fig. 4, which is common to the hypotenuses or bases of the .two prisms l0 and 1.1

will be on the axis XX. The position of the whole system 10, 11 and 12 is finally determined by the condition, that the hypotenuse of the prism'l2 is parallel with the incident faces of prisms 5 and (S. The optical axis of the ocular 9 is then perpendicular to the hypotenuse of the prism 12 and passes through the center of the free upper part of said hypotenuse (Figs. 1 and 25 to 27). Owing 'to the arrangement above referred to, the free side of each prism 10,

11 is struck by one half only of'the rays coming from each objective 7 and 8 respectively.

By observing any object whatever, for

instance that 13, 14 'of Fig. 7, the inverted 'image of it produced by the lens 7 and then inverted as will be later described by the prism 5 will be viewed, as shown partly in full lines ancLpartly in dot-ted lines at Fig.

so 5, on the free" incident face of prism 10.

Owing to ,the limited height of this free face, only the upper part13 (shown in full lines) ofthe image will be inciuded in the free face of the prism 10. This image suc- 05 cessively reflected 5&13", 13, 13 to the hypotenuse of 10 and on the sides of 12 will be produced erected at 13 onthe upper part of the free portion of the emergent face of prism 12. In a similar manner the inverted image of the object 13, 14, produced by lens 8 and then inverted by the prism 6, will be viewed, shown partly in full lines and partly in dotted lines at Fig. 6, on the free incident face of the prism 11. Owing to the height. and position ofsaid face, only a part, in this case the lower part 14 (shown in full lines) of the image will be included in said face. This image successively reflected in 14, 14, 14 will be viewed erected in 1.4" on the lower part of the free portion of the emergent face of the prism 12. Therefore when the images given by the two objectives 7, S, are produced on the same focal. plane and this latter coincides with that of the ocular 9 in which is placed the cross hairs 9 (Figs. 25, 27), the image 13, 1i of the object 13, 14-, will be seen exactly reconstructed in the ocular field (Fig. i though its upper part 13 be due to the objective 7 and the lower one 1 1 to the objective 8. It must be noted here that in order to observe clearly in the ocular field the exact reconstruction of the image 13, l P, a very thin plate 15 must be arranged horizontally outside the ocular (Figs. 1, 25, 27) said plate containing the optical axis of the ocular and projecting from this latter as far as the free emergentface of prism 12 that it divides into two equal portions. It must, however, be noted that the exact reconstruction of the two images 13, 14 into a single image, as shown at Fig. 8, takes place only when-the position of the prisms 5, 6, being ascertainedihe observed object is at a given distance. In any other case the images 13, 14 produced by the two objectives constitute a broken image as shown at Fig. S), namely, if the image 13 is brought to coincide with the vertical wire of the cross hairs, the image 14 will be driven away by a certain amount, in a direct ratio with the displacement of the prisms 5, (3, (telemeter base) and in inverse ratio with the distance. of the object observed. Thus by measuring either directly or indirectly the distance of the images 13, 14, the distance of the object observed may be deduced. It is known that the indirect measurement of said distance in this type of teleineter, is efl'ected by producing the displacement of the two parts of the broken image observed in the ocular field, until a single image corresponding to the object observed is produced. This is obtained either by displacing one of the prisms 5, 6, or by arranging in the path of the rays coming rom one or the other or both the objectives 7, 8, some device capable of producing a suitable deviation of the rays to produce the reconstructed image. The distance of theoliject is of course deduced from the displacement given to one of the prisms 5 or 6, or from the constants of the deviating device inserted on the path of the luminous rays. 7

zlfcasur-z'ng arrangcmcnt.1n the present telemeter we employ for the purpose of measurement, a special arrangeu'ient capable of producing a suitable deviation of the luminous rays coming from one of the obj ectives, which arrangement is based on the following principle: It is known that a prism 16, Fig. 10, bends a luminous ray 17 (which is supposed to be contained in a principal section of the prism, that is in a plane perpendicular to its retracting edge) in the direction 17 (contained in the plane of the same main section) so that the refracted ray strikes a screen 18 at a point 17 different from the intersection point 1%) be tween the projection of said ray 17 and the screen 18. If the prism 17 rotated for instance in the direction of the arrow of the Fig. 11 around an axis perpendicular to the bisecting plane of the retracting angle, the

refracted or deviated ray 17" will also be rotated in the same direction and to the same degree and it the screen 18 is parallel with said bisecting plane the intersection point 17 will make an arc of a circle the center of which is the point 19. If at the side of the prism 16 there is arranged another iden'-- tical prism 20 with the bisecting planeot'its refractory angle parallel to the bisecting plane of the retracting angle of prism .16 and with its retracting edge 180 to the re fracting edge of 16 (Fig. 12), the refracted ray owingto the prism 20 will intersect the plane 18 at 17, While owing to prism 16, it

Will intersect the plane 18 at 17 Owing to the two deviations in reverse directions to Whiclrthe ray 17 has been subjected while passing through the prisms 20, 16, the double efracted ray 17? has the same direction as the initial ray 17 and the intersection 17 with 18 will be at the center of the segment 17 ,17. In other words in this case'the two I prisms 16, 20, operate, as is evident, as a having plane, parallel faces.

It the prisms 16,-20, are now rotated at the same extent and in opposed directions, as shown at Fig. 13, the intersection point 17 is dis- .placed along the/line 21 which is the intersection of the screen 18 with the bisecting plane of the compensating angles formed by the planes of the main section of prisms 20, 16 in which are the" rays 17 and 17 respectively, said plane being always in an un,

variable position in nice owing to the equal and opposite rotations imparted to the prisms 2U, 16. It evident that the inter section 17" t'alls inta-J'point ol' the line .2l, in tact owing to the rotationot prism 20 the refracted ray would meet the screen 18 at 17 "while by effect; of the rotation of the prism 16. ;.sa id retracted ray would Fall at 17", so that owing to the two equal and opposite rotations otthe prisms 16, 20 the retracted ray will intersect the screen 18 at the point 17 which is the center of thesegment 17, 17, perpendicular to the line 21.

From the above it will be understood how the system of two prisms just described is" used in order to produce the deviation of the luminous rays forming one or the other of the parts 13, 11 of the broken image observed in the ocular field of the teleineter (Fig. 9) in order to reconstruct the same in side and both parallel with the emergent face of prism 12 (Fig. 14;). In these conditions the two prisms coiiperate to bend in the same direction the ray 17 which retracted at 17 will intersect at 17 the incident face of prism 11 instead of at the central point 19, which is the intersection of the projection of ray 17 with the incident face of 11. The ray 17 entering 17 will come out at 17 from the emergent face of the prism 12 and in the ocular held 9 the image 17 '(Fig. 15) corresponding to this ray will be seen at the left end of the horizontal diameter of the field. By rotating in opposite directions the prisms 16, 20, through the same angle, the image 17 is displaced by-the rotation of 16 toward 17 (Fig. 15)

and by therotation'of 20 toward 17 the be driven to 17. The displacement 17, 172' undergone by this image is therefore equal to the diminution undergone by the cosine of the angle or when passing from the value zero to the value oi.

From the above'it will be'seen that by rotating the prisms of 'the micrometer in opposite directions and through-tho same angle just described, it is possible. to displace the image 14.(Fig. 9) until it is reconstructed as shown at Fig. 8. It is also evident that from the angle oi rotation a made by each of the prisms 16, 20, during this operation 'it will be possible tocal'culatc the distance of the observed object when the base ot the telemeter, the retracting angles of prisms 16, 20, the refraction index of the substances of which they are composed and their distance from the focal. plane are known, In practice of course instead oi this coijnplicated calculation t'or deducting the distance, scales giving directly the distance corresponding to the rotation undergone by the prisms 16, 20, are'employed.

"One of the numerous constructional practical forms that the micrometer or measur-.

ing device may assume is shown,in horizontal section and in elevation partly-1n section in Figs. 16 and 17 respectively. The

prisms 16, 20, which are preferably achromatic, are mounted on two drums 22,23,

mounted, capable of rotating in supports 24, 25,,eonnected with a base plate 26. In

order to rotate the drums 22,23 in opposite directions the same amount, we may employ any suitable arrangement for instance that represented in the drawing, in which a pinion 27 rotatably mounted in a projection made of two pieces 26, 26", of the base plate 26 and provided with an externally operable knob 28, engages with two toothed face, with a scale having an angular am-- plitude equal to the maximum angle of r0- tation to which each of the prisms 16, 20, may be subjected. This angle, as practice has shown, may be about 100. Figs. 18 to 21 show said scales developed and in different positions. From said figures it appears that corresponding to the'ends of the scales of the drum 23, there is an index for instance with number 12 on one of them; the

other scale commencing with the same figure 12 carries at its beginning another index. The scales are viewed, through a 'slot 35 (shown in dotted lines in Figs. 18 to 21) in the base plate 26; said slot having an angular width a little greater than one half of the angular extent of each scale. When the two drums are displaced as at Fig. 19,

itis the index of the drum 22 (the only one.

that may be seen throughthe slot 35) that will serve to indicate the reading (in Fig. 19, one reads 8). \Vhen the two drums have performed a'rotation corresponding to one half of the maximum rotation, the two inbdexes will be opposite at Fig. 20. If the drums are further rotated, the index of drum 23 will leave the scale and then the reading will be eltected by means of the index of the drum 23 (in Fig. 21 one will read .16).

It will-be noted that in the practice it is preferable to obtain directly from the reading of the scales the distance of the object observed. For this reason the scales are not numbered as shown in Figs. 18 to 21, but in inverted order, namely they begin from the maximum .end to the minimum.

Generally in practice it is required to'measine the distance of an object between 1000 and 6000 meters. Said limits being given by way of'example, we Wlll now describe how the gaging of the instrument effectobject (Fig. 9) will ,be reconstructed into a single image as represented at Fi 8. We mark then at the beginning of t e drum scale 23, 60 hectometer (Figs. 22, 26). By observing then successively objects at lesser distances, the prisms 16, 20, must be rotated for the purpose of reconstructing the broken images into a single image as at Fig. 8. We mark thus successively on the scale of 23 the numbers 59 58 etc., hectometers. When the drum 23 has been rotated through an angle corresponding to one half of the maximum angle, viz. 50, the first portion of the scale 22 is brought back on the drum 22 in correspondence with the last portion of the scale 23, said portion of the scale 22 serving also as an index and in correspondence of which the figure corresponding to the last portion of scale 23, for instance 35 hectometers is marked. Then taking this last portion as index, the scale is continued on the drum 22. In this way we obtain nearly proportional scales. In fact it is evident that the distance between theimages 13", 14, Fig. 9 when passing from 60 to 50 hectometers is much less than the distance between said images when passing for instance from 35 to 34 hectometers. On the other side the displacement imparted to the image 14 owing to the rotation of the prisms of the micrometer is proportional to .the diminution undergone by the cosine of the angle to which each prism has been ro tated and as said diminution is very slow when said angle is included in the first 30 of arc and is very quick when the angle is near .90", the graduations of the scales will be almost equal and the reading will be equally easy when the object is at 60 or a 30 hectometers.

It must now be noted that in practice it is not always possible to effect the observations on an object of considerable height as at Fig. 7. Very often only a point is to be observed; in such case (Fig. 23) it the luminous ray 36 coming from this point through the objective 8 strikes at 36 the incident face of the prism 11 and leaves at the point. 30 of the emergent face of prism 12, the eorrespmiding ray 37 coming from the same point through the objective 7 would strike at 37; now as this face is limited only to the lower part of the luminous conical bundle coming from the objeclive 7 it. would not be possible to see in the upper part of the field of the ocular the image of this point. 'We insert therefore in tive 7 a prism 38 which deviates to 37 the ray 87, which then strikes at 37 the face of 10 and comes out at 37 from the emergent face of 12. I this way the image of the point observed may also be seen in the upper part of the ocular field The measurement of the distance is in this case effected by causing the two i1 ages of the observed pointto coincide with the vertical Wire of the cross hairs. As it is to be preferred, when possible, to point at an object having a certain extent in height, the prism 38 ist-hcn taken off. In order to prevent the shortening that the focal distance of the objective 7 would then undergo, we insert at the place of the prism a glass 39 having parallel plane faces, which corrects this inconvenience. For this purpose the prism and the said glass are mounted at right angles on the same mounting 40 (Figs. 24, 25) on a shaft. 41 parallel with the ocular axis, and capable of rotating on a sleeve 42 fixed to the base plate 26 and. operated from the outside by means of a pin by means of which either the prism 38 or the glass 39 may be placed in operative position;

It is evident that when the plane glass 39 is brought exactly perpendicular to the optical axis XX', it will not cause any deformation of the images. If on the contrary the glass is slightly inclined in respect of said axis, it will produce a lengthening, in the vertical direction, of the image givenby the objective 7 said lengthening may be very useful to facilitate the collimation of the object when its height is limited. In'fact in this case instead of keeping the glass 39 exactly vertical, it is slightly inclined by turning the pin 43 until thedesired effect is attained.

Iieetify-ing arrangement.-Notwithstanding the peculiar form of the mounting, preferably of metal, of the optical pieces of the telemeter and its arrangement inside the casing 4, as above said, the changes of temperature are always dangerously felt especially when they produce a deflection of the telemeter body in a. horizontal plane containing the axis X- X. "The result is to produce a rotation of the prisms 5, 6, on an axis which is parallel with their refracting edge The rectifying arrangen'ient hereafter described serves to bring the prisms 5, (3, again into the position occupied by them during the graduation of the instrument. 'lhe rectifying arrangement (Fig. 23) consists substantially of two little rectangular prisms 4 1-, 45, beveled (at. 4-5 at one of their extremities in order to produce two rcllccting faces I l 45 respectively. These two prisms are placed in a position invariable with respect. to the system .10, 11, 12 and at the opposite sides of this latter, so that the faces 44*, 45 are parallel to the by potenuses of the prisms 10, 11 respectively and will be in that part .of the conical bundle of rays eommg from the objectives 7 and 8 respectively, not occupied by the free sides of the prisms 10 or 11.

()n the bases of'the prisms 44, 45 near the lower edge of one and the upper ed e of the other are engraved scales 44", 45, f 29 showing the whole of the prism. system 10, 11, 12, 44, 45). Besides this the upper and the lower half of the incident faces of the prisms 5 and (3 respectively are silvered, as shown by thefhatched part of Figs. 32 and 28. This will not produce any 111C011- venience in the sight of the images through the. telescopic system already described, as the lower and upper parts of the incident face of the prisms 5 and 6 that cooperate with the prisms 10 and 11 respectively of the erecting system remain quite free. Let us now suppose that on the base of the prism 45, near its upper edge (Fig. 28) be marked for instance a point 46 and this face be lighted in any desired manner. The luminous ray 46 coming from this image and reflected at 46 on the face 45 travelsbelow the optical axis XX, in the direction 46 crosses the lens 8 deviating upward, is reflected at 46 on the. hypotenuse of 6 and.

46, 46 as far as the lens 8, is equal to thefocal distance of 8, it is evident that in the.

lower part of the ocular field 9, owing to the luminous ray coming out at 46 from the face 1.2, the'image of the point 46 Will be seen. It follows that in the lowerpart of the ocular field the scale 45 engraved on the upper edge of the prism base 45 will be Seen. For the same reason the scale 44 engraved on the lower edge of the prism base 44(Figs. 33, 34) will be seenin the upper part of the ocular field.

In Figs. 30. 31, 32, showing a constructional form of the telemeter body, we have shown the objectives 7 and 8, their prisms 5 and (i and the systemof erecting prisms withthe prisms 44- and 45, namely only the parts necessary for the explanation of the working of the rectifying arrangement. The lighting of the bases of prisms 44 and 45 is eflected through suitable slots provided in the block 3 of the telemeter mounting, said slots being kept open only during the rectifying operation. When the graduation of the instrument is completed, by suitably regulating the position of prisms 5 and 6 by means of the screws 3 fixing their mountings to the flanges 2 of the end rings see Fig;

of the telemeter body, the lighting slots of prisms i l and 45 are opened in order to observe in the ocular held the poslticnof the nulled before effecting the measurement.

For correcting this any suitable arrangement may be employed, for instance that shown in the drawing, consisting of a rigid bar 47 attached at its ends to the flanges 2 of the telemeter bo'dy.- A screw 46 screwed 'to the central part 49 of 47 and mounted capable of rotating but'not of sliding along its axis in a. hole, suitably provided in the block 3, serves to produce small deflection in the telemeter body, by'rotating the same in the one or in the other direction. It is therefore possible to eliminate the deflection due to a change of temperature, this being effected by actuating the screw. 48 until the images of the scales 44 45 are brought again into the position shown in Fig. 83 or in register.

Of course the rectifying arrangement above described may be modified in many ways without departing from this present invention. Thus for instance the prisms 44 and 45, in order to realize the condition that their scales 44 and 45 be at a distance from the lenses 7 and 8, equal to the focal distance, by keeping the size of said prisms within reasonable limits, may have a double or triple reflection. In the same manner the arrangement for effecting a deflection of the. telemeter body may be of any other suitable form.

e claim:

1. A telemeter havin a central body portion, frames extendingIongitudinally there from, light receivers rigidly secured at the free ends of the frames, a bar connected to the ends of the frames and means coeperating with bar and body portion to flex the frames.

2. A telemeter having a central body portion, frames extending laterally therefrom, light receivers connected to the ends of the frames and means to flex the framesto cor rect the telemeter for temperature changes.

3. A telemeter having a central body portion, frames extending laterally therefrom comprising flanged bars, and light receivers mounted on the extremities of the flanged bars.

4. A telemeter having a central body portion and frames extending laterally there from comprising bars tapering toward their extremities and light receivers mounted on said extremltles.

5. A telemeter having a central body p0rtion and frames extending laterally thereends and light receivers secured to said ends.

7. A telemeter having a central body portion and frames extendin longitudinally therefrom and increasing in flexibility toward their outer ends, a bar connecting the outer ends and a' screw cooperating with the bar and body portion to flex the frames.

8. A telemeter having a central body portion, frames extending therefrom, light receivers at the extremities of the frames, a prism system in the body to reconstruct the' image from the partial images transmitted by the receivers and optical means at the optical axis of the telemeter to indicate and observe the error due to temperature changes and means to flex the frames to correct said error.

9. A telemeter having a central body portion, frames extending therefrom, light receivers at the outer ends of the frames, a prism system to reconstruct the image from the partial images transmitted by the receivers, a total reflecting prism on each side of said prism system, each having graduations thereon, and means to permit illumination of said prisms independently of the light receivers and means to flexthe frames.

10. A telemeter having a body portion, frames extending therefrom, light receivers at the outer ends thereof, a portion of whose incident faces are formed as reflectors, an image reconstructing prism system in the bc-dy portion, a. total reflecting prism havmg graduations thercon, on each side of the prism system at opposite sides of the optical axis, means to temporarily permit illumination of said prisms independently of the light receivers, and means to adjust the receivers relatively to the prisms to cause the images of the graduations to come into zero register.

11. A fixed base telemeter havipg light receivers, a prism system to recons:ruct a full image from partial images from-the receivers, an ocular cooperating with said system, and a. plate between the ocular and system lying in a plane between the two portions of the reconstructed image.

12. In a telemeter, a prism system comprising a large total reflecting rism and two smaller total reflecting prisms both mounted adjacent to one another on a portion of the hypotenuse of the large prism.

" half of the hypotenuse of thelarger prism,

said. hypotenuse being parallel to the optical axis and theoptical axis passing between the juXt-aposed'faces of the small prisms.

15. In a telemeter the combination-With a frame, light receiversat the ends thereof,

a prism system between the light receivers,

21 pair of oppositely positioned oppositely rotatable distance indicating prisms between one of the recelvers and said system,

a prism and a plane glass' rigidly mounted 15 at right angles to one another and mounted to be turned tl'irough a right-angle between the distance indicating pr sms 'and said system, v

In testimony that We claim the foregoing 20 as our invention, We have signed ournames.

' in presence of t-WG subscribing -itnesses.

. 'naoniio ooLzr. FELICE BARDELIJI.

VVit-nesses:

' FRANCENO Snuom,

Tuoxo l\flARTINA. 

